.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
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.TH GETPAGESIZE 2 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
getpagesize \- get memory page size
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.PP
.B int getpagesize(void);
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getpagesize ():
.nf
    Since glibc 2.20:
        _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
    Glibc 2.12 to 2.19:
        _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
    Before glibc 2.12:
        _BSD_SOURCE || _XOPEN_SOURCE >= 500
.\"        || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
.fi
.SH DESCRIPTION
The function
.BR getpagesize ()
returns the number of bytes in a memory page,
where "page" is a fixed-length block,
the unit for memory allocation and file mapping performed by
.BR mmap (2).
.\" .SH HISTORY
.\" This call first appeared in 4.2BSD.
.SH CONFORMING TO
SVr4, 4.4BSD, SUSv2.
In SUSv2 the
.BR getpagesize ()
call is labeled LEGACY, and in POSIX.1-2001
it has been dropped;
HP-UX does not have this call.
.SH NOTES
Portable applications should employ
.I sysconf(_SC_PAGESIZE)
instead of
.BR getpagesize ():
.PP
.in +4n
.EX
#include <unistd.h>
long sz = sysconf(_SC_PAGESIZE);
.EE
.in
.PP
(Most systems allow the synonym
.B _SC_PAGE_SIZE
for
.BR _SC_PAGESIZE .)
.PP
Whether
.BR getpagesize ()
is present as a Linux system call depends on the architecture.
If it is, it returns the kernel symbol
.BR PAGE_SIZE ,
whose value depends on the architecture and machine model.
Generally, one uses binaries that are dependent on the architecture but not
on the machine model, in order to have a single binary
distribution per architecture.
This means that a user program
should not find
.B PAGE_SIZE
at compile time from a header file,
but use an actual system call, at least for those architectures
(like sun4) where this dependency exists.
Here glibc 2.0 fails because its
.BR getpagesize ()
returns a statically derived value, and does not use a system call.
Things are OK in glibc 2.1.
.SH SEE ALSO
.BR mmap (2),
.BR sysconf (3)
